For purposes of background, the disclosures of the following patent documents are hereby incorporated by reference in their entirety: U.S. Pat. Nos. 4,051,840; 4,630,597; 4,692,148; 4,733,652; 4,809,681; 5,169,379; 5,761,019; 5,833,619; 5,904,666; 6,042,532; 6,132,363; 6,471,633; 6,511,412; 6,735,532; and U.S. patent application Ser. Nos. 10/746,543; 10/770,269; 10/865,965; 11/178,969; and 60/709,323.
The scarcity of human hearts available for transplant, as well as the logistics necessary to undertake heart transplant surgery, make an implantable cardiac assist device the only viable option for many heart patients. An aortic blood pump, for example, can be permanently surgically implanted in the wall of the aorta to augment the pumping action of the heart.
A known aortic blood pump includes a flexible bladder to be inflated and deflated in a predetermined synchronous pattern with respect to the diastole and systole of the patient to elevate aortic blood pressure immediately after aortic valve closure. Inflation and deflation of the bladder is accomplished by means of a supply tube connected to the bladder and to a percutaneous access device (“PAD”). The PAD is permanently surgically implanted in a patient's body to provide a through-the-skin coupling for connecting the supply tube to an extra-corporeal fluid pressure source. Electrical leads from electrodes implanted in the myocardium are likewise brought out through the skin by means of the PAD, The “R” wave of the electrocardiograph is used to control the fluid pressure source to inflate and deflate the inflatable chamber in a predetermined synchronous relationship with the heart action.
The aortic blood pump acts to assist or augment the function of the left ventricle and is typically restricted to use in patients who have some functioning myocardium. The aortic blood pump does not need to be operated all the time, and in fact, can be operated periodically on a scheduled on-time, off-time regimen, or on an as-needed basis. Typically, the patient can be at least temporarily independent of the device for periods of one to four hours or more, depending on their heart function and level of activity. The general structure of known aortic blood pumps is a semi-rigid concave shell, and a flexible membrane that is integrally bonded to the outer surface of the shell, forming an inflatable and deflatable chamber. A fabric layer is then bonded over the exterior surface of the shell that projects clear of the shell forming a suture flange. These blood pumps have been tested and demonstrated to last a few million cycles. None of the known blood pumps disclose or suggest that any modification can be made to the geometry of the shell and membrane to increase the durability of the pump, much less what such modification would be.
A known dynamic aortic patch has an elongate bladder having a semi-rigid shell with walls of uniform thickness and a relatively thicker peripheral edge and a flexible, relatively thin membrane defining an inflatable chamber. At least one passage extends through the shell defining an opening in the inner surface of the shell. The flexible membrane is continuously bonded to the shell adjacent the peripheral side edge to define the enclosed inflatable chamber in communication with the passage. The membrane may have a reduced waist portion, defining a membrane tension zone adjacent to the opening of the passage into the chamber to prevent occluding the opening to the pneumatic supply while deflating the chamber. An outer fabric layer can be bonded to the outer side of the shell of the aortic blood pump, and present a freely projecting peripheral edge to provide a suture flange for suturing the aortic blood pump in place within an incision in the aorta.
Known aortic blood pumps use an inflatable bladder and an envelope. The envelope is sutured to the aorta and then the bladder is placed inside the envelope. Although this design successfully augments the blood pumping capacity of the heart, it has two major disadvantages. First, fluid may accumulate inside the envelope, between the envelope and the inflatable bladder. This accumulation of static fluid within the body commonly leads to infection. Second, due to the geometry of the bladder, the volume of blood displaced by the device is limited, and has been determined to be insufficient.
Experience with patients has shown that it is relatively easy to construct a pump that will last a few million inflation-deflation cycles (on the order of weeks). However, it is very difficult to design, reproducibly manufacture, and implant a pump that will last for at least two years (on the order of a hundred million of inflation-deflation cycles, or more) without membrane failure.
The top surface of the pump's shell can be overlaid with a non-tissue adhesive substance, such as silicone, to prevent scar tissue from adhering to the back of the pump and to allow the pump to be explanted later. But clinical experience has shown that even this improved design may last less than the two-year target in a patient.
Known blood pumps have a suture ring placement that constrains the movement of the blood pump during each inflation-deflation cycle. In these designs, the suture ring is located closely adjacent to the shell bead, in a location outside of the periphery of the shell, and at approximately the same height (measured as the axial distance from the centerline of the aorta) as that of the bead. When the implantation wound heals, the suture line itself, as well as the scar tissue that grows into the suture line, constrain the movement of the shell during each inflation-deflation cycle. This occurrence results in effectively stiffening the shell near the region where it interacts with the membrane, thus forcing the membrane to absorb all of the stress during the inflation-deflation cycles.
The hose barb provides the connection between the internal conduit and the blood pump. Known blood pumps have hose barbs that are glued into place to the back of the shell of the blood pump. This design can be improved to increase the strength of the hose barb's attachment to the shell.
As seen in FIG. 11, the shells of prior art blood pumps are relatively flat across their length, other than slightly turning downwards at the longitudinal ends, and have relatively thin walls of uniform thickness with slightly thicker peripheral edges. However, despite the simplified drawings of aorta in FIGS. 2, 3, and 11, the human aorta is not a straight circular cylinder. Rather, it has a complex three-dimensional shape, sometimes described as a “twisted question mark.” Accordingly, the known flat blood pumps are not well configured to fit to a typical human aorta, and there is a need in the art for a blood pump having a contour that generally matches the contour of a typical human aorta. Further, because of their general cylindrical configuration and relatively thin walls, the permanent deformation of these pumps during surgical implantation into the non-cylindrical aorta can affect their durability.
Thus, although the art discloses the basic concept of an “in-series” mechanical ventricle assist device (blood pump), having a semi-rigid shell, and a flexible membrane, nothing in the art teaches or suggests how to construct a device that will be durable enough to survive inflation-deflation cycles for the number of years desired. To the contrary, clinical experience has shown that the known blood pumps generally last less than the two-year target. Thus, there remains a need in the art for a blood pump design providing increased durability.